Zero-resistance states induced by electromagnetic-wave excitation in GaAs/AlGaAs heterostructures

The observation of vanishing electrical resistance in condensed matter has led to the discovery of new phenomena such as, for example, superconductivity, where a zero-resistance state can be detected in a metal below a transition temperature T_c (ref. 1). More recently, quantum Hall effects were discovered from investigations of zero-resistance states at low temperatures and high magnetic fields in two-dimensional electron systems (2DESs). In quantum Hall systems and superconductors, zero-resistance states often coincide with the appearance of a gap in the energy spectrum. Here we report the observation of zero-resistance states and energy gaps in a surprising setting: ultrahigh-mobility GaAs/AlGaAs heterostructures that contain a 2DES exhibit vanishing diagonal resistance without Hall resistance quantization at low temperatures and low magnetic fields when the specimen is subjected to electromagnetic wave excitation. Zero-resistance-states occur about magnetic fields <ITALIC>B</ITALIC> = 4/5 <ITALIC>B</ITALIC>_{<ITALIC>f</ITALIC>} and <ITALIC>B</ITALIC> = 4/9<ITALIC>B</ITALIC>_{<ITALIC>f</ITALIC>}, where <ITALIC>B</ITALIC>_{<ITALIC>f</ITALIC>} = 2π<ITALIC>fm</ITALIC>*/<ITALIC>e</ ITALIC>,<ITALIC>m</ITALIC>* is the electron mass, e is the electron charge, and f is the electromagnetic-wave frequency. Activated transport measurements on the resistance minima also indicate an energy gap at the Fermi level. The results suggest an unexpected radiation-induced, electronic-state-transition in the GaAs/AlGaAs 2DES.